I explained at the end of the last lecture how to ascertain speedily and certainly whether a graph is absurd or not after the junctures are got rid of. I now give the rule for getting rid of the junctures. Let me repeat that I think there are probably better rules than that which I give; but it is the duty of my students to find these out. My rule, until I learn of a better one is as follows: [??} of a reasoning Perhaps I shall do well to explain set forth to you the line of my thought by which my rule, such as it is, has been derived; because it is comparatively simple, and will give you some rough idea of the kind of reasoning required in establishing a system of logic.

I begin by asking myself, How is it that I need any such rule? The first answer